Teaching Computing Unplugged in Primary Schools by Caldwell Helen;Smith Neil; & Neil Smith

Author:Caldwell, Helen;Smith, Neil; & Neil Smith
Language: eng
Format: epub
ISBN: 5601731
Publisher: SAGE Publications, Limited
Published: 2017-08-15T00:00:00+00:00

Figure 5.5 Polybius square

To decrypt the ciphertext you need to know the grid used and if any (and which) of the letters of the alphabet have been combined into a single cell. Then use the grid references to turn the ciphertext into plaintext.

Student resource: www.digitalschoolhouse.org.uk/sites/default/files/cms/docs/Clue%201.docx

Resource answers: www.digitalschoolhouse.org.uk/sites/default/files/cms/docs/Clue%201%20Answers.docx

Reverse cipher

The reverse cipher method works by reversing the order of the string of characters in the plaintext to create the ciphertext. For example: ‘Code Breakers’ becomes ‘srekaerB edoC’. This is possibly the simplest method encryption and the easiest method to crack. You can make it harder to crack by removing both the capitalisation of letters and the spaces. For example, ‘Code Breakers’ becomes ‘srekaerbedoc’. Although this is an improvement, it is still relatively easy to crack. To make it a bit harder to crack by further disguising the plaintext, you can do this by grouping the ciphertext string of characters into groups. For example, ‘Code Breakers’ becomes ’sre kae rbe doc’. To support the pupils with this activity, it is best to give them centimeter squared paper to record the plaintext and ciphertext.

Student activity resource: http://northofsepo.wikidot.com/activity:reverse-cipher

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